The Case for Keeping Colonoscopy

Dec. 17, 2008

Reporter's Notebook by ROGER SERGELABC News Medical Unit

When a story breaks in The New York Times about a major health issue, such as colon cancer, we pay attention. So when Gina Kolata had a story Tuesday morning with the headline "Colonoscopies Miss Many Cancers, Study Finds," we needed to take a look.

The Times reported that a Canadian study published in the Annals of Internal Medicine had concluded that the common test, which scans the inside of the colon for cancers, "missed just about every cancer in the right side of the colon, where cancers are harder to detect but is where about 40 percent arise."

"And it also missed roughly a third of the cancer in the left side of the colon," the report said. "Instead of preventing 90 percent of cancers, as some doctors have told patients, colonoscopies might actually prevent more like 60 [percent] to 70 percent."

ABC News medical editor Dr. Tim Johnson discussed the story briefly on "Good Morning America," but he focused more on practical questions, such as the need for complete bowel preparation.

We had seen a summary of the study Monday and nothing suggested as dramatic a finding as the Times story. What made the Times story sound so worrisome were the phrases such as "much less accurate than anyone expected" and quotes that included "a shock," "a really dramatic result" and "it makes you step back and worry, 'what do we really know?'"

So we used the network of experts we regularly e-mail and took another look at the study.

A Closer Look at Colonoscopy

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We asked three questions of three groups: colorectal surgeons, gastroenterologists and primary-care physicians. We wanted to know what primary-care physicians thought because there was a suggestion that perhaps the Canadian study did not reflect the best quality colonoscopy because only one-third of the doctors who did the procedure were gastroenterologists.

We asked these questions:

1. What was their view of whether the statement by Gina Kolata was an accurate summary of the study?

2. What were their views on the limitations of the study?

3. What is their advice to people about bowel preparation?

We expected to hear about "shock" and fears of the procedure being less accurate than thought. We did not hear that.

On the "90 percent" expectation figure, Dr. Dennis Ahnen, gastroenterologist and staff physician at the Denver VA Medical Center, said that this effectiveness statistic comes from the National Polyp Study done in the United States.

What this study found was that subjects whose polyps had been removed once they were found through a colonoscopy (a procedure called colonoscopic polypectomy), and who were subsequently monitored by their doctors for additional polyps, had a 75 percent to 90 percent or so decreased risk of subsequent colorectal cancer compared to historic control groups.

"There are, however, several other study groups that have had colonoscopic polypectomy and surveillance who have not had nearly as a beneficial effect as those in the National Polyps study and are more consistent with the results of the Annals paper," Ahnen said.

In other words, there are plenty of studies that suggest the effectiveness may be lower than 90 percent.